Protective helmets may be classified differently depending upon the requirements imposed upon the helmet. In order that a helmet be referred to the highest class, certain countries stipulate that there must be no bolts or holes piercing the shell of the helmet. Through-bolts are considered as a safety risk, as they can conduct electric current from the outside of the shell to its inside. The need to dispense with the use of such bolts brings about certain difficulties with respect to the attachment of various accessories to the helmet. This applies for instance to the mounting of a face shield, which must be pivotable between two positions, one active position in front of the face, and one retracted, rest position. It is furthermore important that the face shield is designed so as to permit an easy mounting and dismounting, as it is desirable to remove the shield when it is not required for the work at hand, and it furthermore is advantageous to be able to substitute one shield for an other, as called for by the work to be performed.